1. Field of the Invention
The present invention relates to an apparatus for detecting defective sewing by the sewing machines, which is configured to detect the quantity of light transmitted through a cloth passing over a needle plate during sewing operation in order to check for defective sewing from increase and decrease of said transmitted light.
2. Description of Prior Art
When a cloth is sewed by a sewing machine, defective sewing such as misalignment and plyshift are liable to take place. Misalignment, as shown in FIG. 4, is such that cloths W1, W2, placed one over the other, are shifted along the direction of the arrow X orthogonal to the forward sewing direction, that is, the direction of the arrow Y going along the cloth feeding direction F, and thereby, side ends W1a, W2a of the cloths W1, W2 become uneven with each other. Plyshift, as shown in FIG. 5, is such that the cloths W1, W2 are shifted along the direction of the arrow Y, and thereby, terminal ends W1b, W2b of the cloths W1, W2 become uneven with each other. In order to obtain well-finished sewing products, it is required to quickly detect occurrence of defective sewing such as misalignment and plyshift during sewing operation.
To meet such requirement, there is a conventional proposal of an apparatus for detecting defective sewing by the sewing machines as is disclosed in Japanese Utility Model Publication No. 59-25349. This apparatus comprises a sensor which is located at a side of a needle drop portion of a needle plate and serves to detect the quantity of light transmitted through a cloth passing over the needle plate, and a control circuit which serves to determine with or without defective sewing from increase and decrease of said light quantity. And in this apparatus, the inspection light is projected on one side of the surface and the back of the cloth passing over the needle plate, and the inspection light passing through the cloth is received at the other side of the cloth, and thereby, the increase and decrease of the received light quantity are determined to detect defective sewing.
However, in the case of using an optical transmission type sensor as described above, the quantity of the inspection light passing through the cloth varies depending upon the properties of the cloth such as thickness, material and color. Accordingly, in a conventional apparatus using such the optical transmission type sensor, it is necessary to make the adjustment of the reference transmission level, that is, to adjust the sensibility of the sensor by executing a test sewing operation before start of sewing the intended cloth, therefore, extra time is spent and the operation efficiency can not enhance.
Also, in a conventional apparatus, when defective sewing is detected, occurrence of defective sewing is informed to the operator by giving a warning sound, but the warning sound is a single sound and, therefore, it is difficult to identify the sewing machine in sewing trouble when a plurality of machines equipped with relevant apparatus are operated adjoining to each other. Further, in a conventional apparatus, it is unable to cancel the detection of defective sewing and to meet requirements for sewing special products.
It is an object of the present invention to provide an apparatus for detecting defective sewing by the sewing machines, that is capable of detecting defective sewing precisely and performing immediately the practical sewing while improving the operation efficiency without need of adjusting the sensitivity of the sensor by test sewing or the like even in case of sewing cloths different in properties.
It is another object of the present invention that the sewing machine occurring defective sewing identifies quickly even when a plurality of sewing machines are operated at the same time.
To achieve the object, the apparatus includes a sensor for detecting the quantity of light transmitted through a cloth passing over a needle plate, and a control circuit for checking occurrence of defective sewing from increase and decrease of said light quantity. The sensor is disposed near a needle drop portion of the needle plate. A feature of the present invention is that the control circuit comprises means for storing the average value of the light quantity transmitted in a few stitches of initial sewing operation, and means for determining defective sewing during sewing operation continuously the initial sewing operation by comparing the stored average value with the value of the quantity of light transmitted and detected each time.
According to the present invention having the above configuration, when cloths set on the needle plate are sewn while passing through the needle drop portion, the quantity of light transmitted through the cloth is detected by a sensor near the needle drop portion. In that case, the storing means of the control circuit stores the average value of the quantities of light transmitted through the cloth in a few stitches of initial sewing operation. And in subsequent sewing operation, the value of the quantity of light transmitted and detected each time is compared with the stored average value of the quantities of transmitted light, thereby detecting defective sewing, that is, occurrence of trouble such as misalignment and plyshift. As a result, even when every cloth to be sewn is different in properties such as thickness, material, and color, it is possible to start the practical sewing immediately without taking much time and trouble for doing extra jobs such as adjusting the sensitivity of the sensor, and to precisely detect defective sewing, simultaneously improving the operation efficiency.
In this apparatus having the above configuration, the control circuit includes warning means for generating a warning sound in case of detecting defective sewing and a selective operation member which can change the warning sound from the warning means to a different kind of warning sound. In this way, when a plurality of sewing machines adjoining to each other are operated at the same time, the warning sound can be changed to a different kind of warning sound every sewing machine through the selective operation member, and thereby, it is possible to quickly and surely identify the sewing machine occurring defective sewing.
Also, in this apparatus having the above configuration, the control circuit includes further an invalid section setting member which can invalidate the detection of defective sewing during sewing operation in a predetermined section. In this way, since it is possible to invalidate the detection of defective sewing during sewing operation in the predetermined section, unnecessary detection of defective sewing and resultant generation of a warning sound can be avoided in sewing of special products, which includes a form of sewing section similar to misalignment or plyshift, and thereby, the intended special sewing can be appropriately performed.
The other objects and advantages of the present invention will be made clear in the following description of the embodiments.